1. Technical Field of the Invention
The present invention relates generally to a fuel injection control apparatus, such as a common rail system for automotive diesel engines, which is designed to inject fuel into a cylinder of an internal combustion engine through a sequence of multiple injection events in each operating cycle of the engine, and more particularly, to such an apparatus deigned to increase the number of injection events to minimize a combustion noise of the engine.
2. Background Art
Typical diesel engines for automotive vehicles to required not only to meet tightened exhaust regulations, but also to reduce noise arising from combustion of the engine which is usually higher than that in gasoline engines. The reduction in noise is proposed to be achieved using a multi-injection strategy in which a sequence of multiple injection events are performed in each operating cycle of the engine (i.e., a four-stroke cycle) including intake or induction, compression, combustion, and exhaust. Specifically, the more the number of injection events, the smaller will be the amount of fuel sprayed in each of the injection events, thus resulting in a decrease in the degree of combustion to reduce the combustion noise. For example, Japanese Patent First Publication No. 5-195848 teaches such a technique. Consequently, it is preferable to increase the number of injection events in each operating cycle of the engine as many as possible.
To achieve the multi-injections, fuel injection systems are usually employed which are designed to store the fuel in an accumulator or common rail under high pressure and spray the fuel, as stored in the common rail, into the engine through injectors. Such a type of fuel injection system is equipped with an injector drive circuit which works to energize or open each of the injectors in accordance with an injection pattern defining a fuel injection mode. Specifically, the injector drive circuit is equipped with a capacitor and an electrical charger. When it is required to initiate the injection of fuel into the engine, the injector driver circuit release electrical energy, as stored in the capacitor by the capacitor charger, to open each of the injectors quickly to achieve the fuel injection mode, as defined by the injection pattern.
The injector drive circuit is, however, usually elevated in temperature due to cyclic execution of the fuel injections. Specifically, when the capacitor is discharged or charged, a large current will flow in the injector drive circuit, so that it generates a large amount of heat and increases the temperature of the injector drive circuit. In order to avoid a reduction in performance of the injector drive circuit arising from a rise in temperature thereof, the number of injections to be executed in each operating cycle of the engine needs to be limited.